PROJECT SUMMARY Diabetic retinopathy (DR) is a leading cause of blindness in the US and one of the major complications of both Type 1 and Type 2 diabetes. Although DR is widely accepted to be an ischemia-driven disease, the current diagnosis and grading of DR severity is based solely on anatomic alterations such as the quantification of abnormal retinal microvasculature in non-proliferative disease or angiogenesis in proliferative stages. As a result, retinal impairment is irreversible in most DR patients when diagnosed, largely due to the lack of technology to quantify retinal ischemia and the lack of knowledge of the underlying mechanism of retinal ischemia. This proposal aims to investigate retinal ischemia in early diabetes using a novel optical coherence tomography technology, which offers the capability to quantify metabolic rate of oxygen (MRO2) in the retina for the first time. We refer to this new technology as visible-light optical coherence tomography or vis-OCT. We seek to identify when MRO2 alterations initially occur, the causes of MRO2 alterations, and whether intervention of MRO2 affects the development of DR in a unique Type 1 mouse model. At the end of the project period, we will have 1) established a time line and mechanistic knowledge of retinal MRO2 changes during the development and progression of DR and 2) fully-optimized the vis-OCT system that is ready to be translated for the next-stage patient testing.